As shown in FIG. 1, a lighting luminance of a lighting apparatus that is driven by an AC (alternating-current) power supply is known to have fluctuations at, for example, a frequency twice as large as an AC frequency thereof (50 Hz etc.). In such a situation, when imaging is performed with a CMOS (Complementary Metal Oxides Semiconductor) image sensor, an image obtained as a result of the imaging may have blinking stripes in a row direction (horizontal direction) as shown in FIG. 2. In general, this phenomenon is called flicker. The flicker is generated because the CMOS image sensor performs imaging by rolling shutter in which an exposure timing is shifted on a row by row basis.
In this regard, various proposals to cope with the flicker have been made in the past.
For example, Patent Literature 1 describes the invention in which an exposure time of a global shutter is set to be the integral multiple of a flicker period (fluctuation period of lighting luminance), to equalize fluctuations of the lighting luminance in the exposure time of each row and suppress the generation of the flicker. In this invention, however, since the exposure time depends on the flicker period, the exposure time for each row cannot be set to be shorter than the flicker period.
Further, Patent Literature 2 describes the invention in which frames captured in accordance with time corresponding to one phase of the flicker period are integrated to estimate a flicker-cancelled luminance state, and an estimation result and the current frame are compared to extract and correct a flicker component of the current frame. However, this invention cannot cope with flicker of a long period.
Additionally, Patent Literature 3 describes the invention in which an image of a long exposure time and an image of a short exposure time are sequentially captured, and a difference in luminance integration value is extracted for each row as flicker component and corrected.